I asked it for references about Hafez Shirazi’s abandoned journey to India and it suggested a very specific Encyclopaedia Iranica entry which seemed perfect, and of course did not exist.
> Provide me with references about Hafez Shirazi’s abandoned journey to India. Answer "I don't know" if you are not 95% certain they exist.
It said "I don't know". I asked it with the same prompt but for a thing I know has references and those were real.
Not guaranteed to work but better results if you want greater certainty.
Technically, this could be read as == instead of >=, meaning it should answer "I don't know" when it is 99% or 100% certain...